A difficulty with forming of different kinds (whether under pressure alone such as drawing (deep or shallow) and imprinting, or pressure and temperature such as injection moulding, blow moulding, extrusion, vacuum forming, thermoforming, pressure forming, compression moulding (e.g. for rubber or cross-linkable materials) vacuum forming in conjunction with material extrusion, thermoforming in conjunction with extrusion and/or vacuum forming, calendaring and post processing and similar forming processes) is the need to ensure an ability for the apparatus
(i) to meet tolerances required,
(ii) to be brought to its operating conditions without fouling,
(iii) to be operated whether at operating temperature(s) or not without destructive interferences, and
(iv) to be brought to the forming zone (preferably a pressure zone) with or without any tracked or guided movement opening and then closing gaps that capture unwanted material.
It is to at least some of those features (i) to (iv) that the present invention is in some aspects directed.
A difficulty, for example, in mating or co-acting dies or other forming tools (“forming tools”) is the prospect of undesired gaps and variations in orientation over the forming zone (hereafter “pressure forming zone”). This is irrespective of whether or not the forming tools simply receive material under pressure (e.g. injection moulding) or apply pressure to a material not being introduced under pressure (e.g. extrusion and then thermoforming), or some hybrid thereof, as there is the prospect of material being entrapped between adjacent forming tools and thereby giving rise to inferior production and excessive stresses and pressure(s) in the system. Any progression of forming tools about a curve will affect orientations and interferences. For example a prior art method (or alternative) of moving consecutive or continuous die blocks into position is shown in FIG. 3a (for example a pipe forming caterpillar). The blocks are attached on a continuous linkage, for example conveyor belt chain or otherwise, and are driven about the circuit. As they come in to meet with each other a nip point A is formed between consecutive blocks prior to them coming into parallel alignment. The presence of such a nip point creates, as can be appreciated, problems and join lines in the finished product.
In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.
It is to features of thermal control and/or fouling prevention that in some aspects the present invention is directed. It is an additional or alternative object of the present invention to provide forming apparatus able to be operated on a continuous or substantially continuous basis by providing requisite pressures over a pressure forming zone between co-acting forming tools or at least to provide the public with a useful choice.